Elastic shaft joint

ABSTRACT

An elastic shaft joint comprises a shaft with a pair of outer-diameter side engagement surfaces which are substantially parallel to each other at two positions on the opposite sides of the outer peripheral surface in the radial direction, a rotary member with a pair of restraint plate portions which are substantially parallel to each other, having an opening on a lateral side thereof, and a vibration absorbing member provided between the rotary member and the shaft. The vibration absorbing member is constituted by an elastic member disposed on the inner peripheral surface of a part fixed to the rotary member and a sliding sleeve which is supported by the inner peripheral surface of the elastic member and which inner peripheral surface is in slidable contact with the outer peripheral surface of the shaft.

[0001] This application claims the benefits of Japanese Application Nos.10-163276, 11-046551 and 11-085415 which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an elastic shaft joint which isassembled into a universal joint for constituting, for example, asteering apparatus for a car so as to transmit a motion of a steeringwheel to a steering gear and to prevent a vibration on the side of thesteering gear from being transmitted to the steering wheel.

[0004] 2. Related Background Art

[0005] A steering apparatus for a car is arranged to transmit a motionof a steering shaft which is rotated by a steering wheel to a steeringgear so as to give a steering angle to the wheels. Normally, thesteering shaft and the input shaft of the steering gear can not bedisposed on the same straight line. For this reason, a universal jointis arranged between the steering shaft and the input shaft to transmit amotion of the steering wheel to the steering gear. A vibration absorbingability is conventionally given to the universal joint, in order toprevent the vibration which is transmitted from the wheels to thesteering gear when the car is run from further being transmitted to thesteering wheel to give unpleasant feeling to the driver. In order togive the vibration absorbing capability to the universal joint in thismanner, an elastic material such as rubber is usually assembled intothis universal joint so that the transmission of the vibration isprevented by use of the elastic material.

[0006] As such an elastic shaft joint or a universal joint assemblingsuch elastic shaft joint therein, there are conventionally known jointsdisclosed in Japanese Patent Application Laid-Open Nos. 56-39325 (FrenchPatent Application Laid-Open No. 2464404), 56-131831, 60-184716 to60-184718, 60-215122, and 60-215123, 61-201924, Japanese Utility ModelApplication Laid-Open Nos. 54-82257, 5-83462, and 5-89964, French PatentApplication Laid-Open No. 2614985, U.S. Pat. No. 4,509,775; etc.

[0007] In the elastic shaft joint conventionally known, leaving the casein which a vibration in the direction of rotation of the shaft such as asteering shaft is applied, when a vibration in the axial direction ofthis shaft is applied, the capacity of the shaft joint to attenuate thisvibration is poor, so that the vibration in the axial direction iseasily transmitted to the steering wheel. Especially, when adisplacement along the axial direction is applied to a part with a shaftmounted thereon, for example, when the distance between the steeringgear and the front end portion of the steering shaft is changed due to avibration upon running of the car, this displacement can not beabsorbed. Also, if it is required to absorb an tolerance inmanufacturing or assembling the parts when the elastic shaft joint is tobe assembled into a steering apparatus of the car, such requirement cannot be satisfied. Further, when one end portion of the shaft with theelastic shaft joint assembled therein is inserted in the base endportion of a yoke of a universal joint in the axial direction thereof,this end portion of the shaft is required to be displaced in the axialdirection, which also can not be satisfied.

[0008] Taking these circumstances into account, such a structure asdisclosed in, for example, Japanese Patent Application Laid-Open No.11-048991 is contrived in which a shaft is divided into a pair ofelements and the paired. elements are brought into serration engagementwith each other at a coupling portion thereof. Since the portion of theserration engagement between the paired elements allows a largedisplacement in the axial direction, even when a displacement in theaxial direction is applied onto a portion with the shaft mounted thereonupon running of the car, this displacement is absorbed. If an tolerancein manufacturing or assembling of the parts is required to be absorbedwhen the elastic shaft joint is to be assembled into the steeringapparatus of the car, it is possible to prevent such tolerance. Further,when one end portion of the shaft with the elastic shaft joint mountedthereon is to be inserted into the base end portion of the yoke of theuniversal joint in the axial direction, it is possible to displace thisend portion of the shaft in the axial direction.

[0009] However, the cost is inevitably increased when the serrationengagement portion is provided in a part of the shaft. That is, in orderto prevent a backlash of the serration engagement portion, irrespectiveof presence or absence of vibration in running, it is required to form aslit on the side of an outer shaft on which a highly accurate processingis performed or a female serration is formed, for elastically expandingor contracting the diameter of this outer shaft. Further, it is requiredto provide a weight member for elastically contracting the diameter ofthe outer shaft.

SUMMARY OF THE INVENTION

[0010] Taking these circumstances into consideration, an object of thepresent invention is to provide a practical elastic shaft joint which iscapable of absorbing a displacement in the axial direction and securinga sufficient durability though manufactured comparatively at a low cost.

[0011] The elastic shaft joint of the present invention is to couple anend portion of a rotatable shaft such as a steering shaft and a rotarymember which rotates upon rotation of such shaft, such as a yoke forconstituting a universal joint, so as to absorb a certain displacementin the axial direction of the direction of rotation.

[0012] Out of such elastic shaft joints of the present invention, anelastic shaft joint according to a first aspect of the invention has apair of outer-diameter side engagement surfaces which are substantiallyparallel to each other at two positions on the opposite sides of theouter peripheral surface in the radial direction. The rotary member isprovided with a pair of restraint plate portions which are substantiallyparallel to each other and is formed to have an opening on a lateralside thereof. Then, a vibration absorbing member is provided between therotary member and the shaft. Then, this vibration absorbing member isconstituted by an elastic member which is disposed on the innerperipheral surface of a part fixed to the rotary member and a slidingsleeve which is supported by the inner peripheral surface of thiselastic member, which inner peripheral surface is brought into slidablecontacted with the outer peripheral surface of the shaft.

[0013] An elastic shaft joint according to a second aspect of thepresent invention is provided with a coupling sleeve around one end ofthe shaft, to allow free displacement of this shaft in the axialdirection and to freely absorb a vibration to be transmitted to or fromthis shaft. Of the rotary member, the base portion, to which an endportion of the shaft is to be coupled and fixed, is formed to have anopening on the lateral side thereof. Then, this coupling sleeve iscoupled and fixed to this rotary member to form the elastic shaft jointby inserting the coupling sleeve into this base portion from the lateralopening so as to suppress the coupling sleeve by means of this baseportion.

[0014] Further, an elastic shaft joint according to a third aspect ofthe present invention is provided with a pair of outer-diameter sideengagement surfaces which are substantially parallel to each other attwo positions on the opposite sides of the outer peripheral surface inthe radial direction of at least one end portion of the shaft.

[0015] A coupling sleeve is disposed in the vicinity of an end portionof the shaft. Then, rotation limiting cylinders are provided at twopositions on the inner peripheral surface on the opposite sides in theradial direction, in a half part of this coupling sleeve in the axialdirection which is a part closer to the end portion of this shaft. Eachof these rotation limiting cylinders is provided with inner-diameterside engagement surfaces which are substantially parallel to each otherand face the above-mentioned outer-diameter side engagement surfaceswith a gap therebetween in a neutral state in which no phase shift isgenerated with respect to the direction of rotation between the shaftand the coupling sleeve, so as to limit an amount of rotation of theshaft within the coupling sleeve. On the other hand, a retainingcylinder having a larger diameter than that of the rotation limitingcylinder is provided in the other half part of the coupling sleeve inthe axial direction, which is a part closer to a middle portion of thisshaft. Between the inner peripheral surface of this retaining cylinderand the outer peripheral surface of the end portion of the shaft, thereis provided a vibration absorbing member which prevents the transmissionof a vibration to and from the coupling sleeve in the above-mentionedneutral state, but allows displacement of the shaft in the axialdirection with respect to this coupling sleeve.

[0016] Further, out of the rotary member, the base portion to which oneend portion of the shaft is to be coupled and fixed is provided with apair of restraint plate portions which are substantially parallel toeach other and is formed to have an opening on the lateral side thereof.Then, in a state in which the rotation limiting cylinder out of thecoupling sleeve is inserted between these two restraint plate portionsfrom the lateral opening, parts closer to the opening ends of theserestraint plate portions are coupled to each other by means of a bolt soas to suppress the both restraint plate portions toward each other,thereby connecting and fixing the coupling sleeve to the rotary member.

[0017] More preferably, one or more of the following structures (1) to(4) are added.

[0018] (1) An shock absorbing member for absorbing an energy of animpact, when the impact is applied in the axial direction, is providedin series with respect to the above-mentioned shaft, to contract thetotal length of the shaft.

[0019] (2) A stopper is disposed between the rotation limiting cylinderand the shaft for restricting a displacement in the axial direction ofthe rotation limiting cylinder and the shaft within a predeterminedrange to prevent the shaft from being drawn out of the shaft.

[0020] (3) Sealing members for preventing foreign substances fromadvancing into the coupling sleeve are provided between the opening endportions of the retaining cylinder and the outer peripheral surface ofthe middle portion of the shaft and at the opening end portion of therotation limiting cylinder.

[0021] (4) Locking portions are provided on the lateral portions of thepaired restraint plate portions for constituting the base portion of therotary member, while the coupling sleeve is provided with an insertionplate which can freely advance to parts opposite to these lockingportions and, after the advancement, is prevented from coming off fromthese parts opposites to the locking portions on the basis of anengagement with these locking portions, and an elastic stretching piecewhich is protruded from the opening side of the pair of restraint plateportions out of the peripheral surface of the coupling sleeve, so thatthe coupling sleeve can be freely pressed to the interior part of thebase portion on the basis of the engagement between the outer peripheralsurface of the middle portion of the coupling member, which couples therotary member to the coupling sleeve by reducing a distance between thepaired restraint plate portions.

[0022] The effect obtained when a rotating force is transmitted bypreventing transmission of a vibration by means of the elastic shaftjoint according to the second aspect of the invention, out of theelastic shaft joints of the present invention constructed as describedabove, is as follows. Even in case of transmission of the rotationalforce, if the rotational force to be transmitted is of low torque, therotational force is transmitted via the vibration absorbing member. Whenthe rotational force to be transmitted is of low torque as described orwhen the rotational force is not transmitted, the vibration absorbingmember prevents the transmission of the vibration between the couplingsleeve which is coupled and fixed to the rotary member, and the shaft.The vibration and displacement in the axial direction is absorbed whenthe vibration absorbing member is displaced in the axial direction orthe vibration absorbing member and the shaft slide each other.

[0023] Also, when the torque of the rotational force to be transmittedis large, the pair of outer-diameter side engagement surfaces formed onone end of the shaft are brought into contact with the inner-diameterside engagement surfaces, and the rotational force is transmittedbetween the shaft and the rotary member to which the coupling sleeve isfixed. That is, the rotational force which can not be transmitted by thevibration absorbing member is transmitted by a contact portion betweenthe outer-diameter side engagement surfaces and the inner-diameter sideengagement surfaces. As a result, an excessive stress is not appliedonto this vibration absorbing member, so that the durability of thisvibration absorbing member can be sufficiently secured.

[0024] Since the rotary member and the coupling sleeve are coupled toeach other by inserting the rotation limiting cylinder of this couplingsleeve between the pair of weight plate portions for forming this rotarymember from the lateral opening thereof, this coupling work is nothindered even if there is a little gap between the axial position of therotary member and that of the coupling sleeve. Also, it is not necessaryto displace the shaft in the axial direction at the time of thiscoupling work. Consequently, there is no need to employ an expensivestructure such as a serration engagement portion or the like.

[0025] If the shock absorbing member is provided, as stated in (1)above, it is possible to ease the impact which is applied to the body ofthe driver from the steering wheel at the time of crash accident,thereby protecting the driver more effectively.

[0026] Also, as stated in (2) above, if a rough engagement portion isarranged between the rotation limiting cylinder and the shaft, it ispossible to prevent the shaft from falling off from this rotationlimiting cylinder at the time of conveyance, thereby saving a troublecaused by the separation of the coupling sleeve from the shaft.

[0027] Also, as stated in (3) above, if the sealing members are arrangedbetween the opening end portion of the retaining cylinder and the outerperipheral surface of the middle portion of the shaft, and at theopening end portion of the rotation limiting cylinder, it is possible toprevent foreign substances such as water or dust from advancing into thecoupling sleeve, thereby preventing rust on the outer peripheral surfaceof one end portion of this shaft or increase of a sliding resistance ofthe sliding portion.

[0028] Further, as stated in (4) above, if, in the state in which thecoupling sleeve is thrust into the interior part of the base portion ofthe rotary member, the coupling sleeve is arranged not to be drawn fromthe base portion owing to the engagement between the insertion plate andeach of the locking portions, and moreover, the coupling sleeve isarranged to be urged upon the interior part of the base portion owing tothe engagement between the outer peripheral surface of the middleportion of the coupling member and the elastic stretching piece, a workfor coupling the shaft with the coupling sleeve mounted thereon to therotary member can be conducted easily while making the center ofrotation of one member corresponding to that of the other member.

BREIF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a side view for showing a first embodiment of thepresent invention, in a state that the elastic shaft joint is in theprocess of assembling.

[0030]FIG. 2 is a view showing a cross section taken along line 2-2 inFIG. 1, in a state that the joint has been assembled.

[0031]FIG. 3 is a cross-sectional view of the joint taken along line 3-3in FIG. 2.

[0032]FIG. 4 is a view showing a cross section taken along line 4-4 inFIG. 2, in a state that the joint is in the process of assembling.

[0033]FIG. 5 is a partial cut-away side view for showing a secondembodiment of the present invention, with a part omitted therefrom.

[0034]FIG. 6 is a side view for showing a third embodiment of thepresent invention, with a part omitted therefrom.

[0035]FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 6.

[0036]FIG. 8 is a partial cut-away side view for showing a fourthembodiment of the present invention, with a part omitted therefrom.

[0037]FIG. 9 is a cross-sectional view taken along line 9-9 in FIG. 8for schematically illustrating bellows.

[0038]FIG. 10 is a cross-sectional view taken along line 10-10 in FIG.8.

[0039]FIG. 11 is a partial cut-away front view for showing a fifthembodiment of the present invention, seen in the same direction as FIG.2, with a bolt omitted therefrom.

[0040]FIG. 12 is a cross-sectional view taken along line 12-12 in FIG.11, showing a state in the process of assembling, with a part omittedtherefrom.

[0041]FIG. 13 is a side view for illustrating a yoke with a weightbracket attached thereto, in an enlarged manner.

[0042]FIG. 14 is a side view for illustrating a shaft with a supportedbracket attached thereto, in an enlarged manner.

[0043]FIG. 15 is a partial cut-away front view for showing a sixthembodiment of the present invention, seen in the same direction as FIG.2.

[0044]FIG. 16 is a cross-sectional view taken along line 16-16 in FIG.15, showing a state in the process of assembling, with a part omittedtherefrom.

[0045]FIG. 17 is a view for illustrating a yoke only in an enlargedmanner, seen from below.

[0046]FIG. 18 is a side view for illustrating a shaft with a supportedbracket attached thereto, in an enlarged manner.

[0047]FIG. 19 is a partial cut-away front view for showing a seventhembodiment of the present invention, seen in the same direction as FIG.2.

[0048]FIG. 20 is a side view for illustrating a base portion for formingthe yoke only, in an enlarged manner.

[0049]FIG. 21 is a view seen from the right side of FIG. 20.

[0050]FIG. 22 is a partial cut-away front view for showing an eighthembodiment of the present invention, seen in the same direction as FIG.2.

[0051]FIG. 23 is a cross-sectional view taken along line 23-23 in FIG.22, showing a state in the process of assembling, with a part omittedtherefrom.

[0052]FIG. 24 is a partial cut-away front view for showing a ninthembodiment of the present invention, seen in the same direction as FIG.2.

[0053]FIG. 25 is a cross-sectional view taken along line 25-25 in FIG.24, showing a state in the process of assembling, with a part omittedtherefrom.

[0054]FIG. 26 is a side view for illustrating a coupling bracket fixedto an end portion of the shaft, seen from below.

[0055]FIG. 27 is a view seen from the right side of FIG. 26.

[0056]FIG. 28 is a side view of an inner periphery of a sleeve elementaccording to a tenth embodiment of the present invention.

[0057]FIG. 29 is a cross-sectional view taken along line 29-29 in FIG.28.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] FIGS. 1 to 4 show a first embodiment of the present invention. Inthis embodiment, an elastic shaft joint 3 of the present invention isconstituted by a yoke 1 of a universal joint for forming a steeringapparatus of a car, and a shaft 2 to be coupled to this yoke 1. The yoke1 which is corresponding to the rotary member described above isprovided with a base portion 4 which is formed from a steel plate byplastic working such as bending and punching with a press or forging.This base portion 4 has a pair of restraint plate portions 5, 5 whichare substantially parallel with each other and integrally formed at oneend thereof, and is formed to be open at the other end, that is, at alateral side thereof, to have a U-shaped cross section. A pair of arms6, 6 are formed to be extended from the front end edge portions of theparallel restraint plate portions 5, 5 for forming such base portion 4in the axial direction (the left end edge portions in FIGS. 1 and 2).Another yoke 9 is rockably coupled to the front end edge portions of thepaired arms 6, 6 via a cross shaft 7 and needle bearings 8, 8, therebyforming a universal joint of a Cardan type. The elastic shaft joint ofthe present embodiment is assembled in such universal joint to couple anend portion of the shaft 2 which rotates upon an operation of thesteering wheel and the yoke 1 which rotates upon rotation of this shaft2 so as to absorb a certain displacement in the axial direction and thedirection of rotation.

[0059] Such an elastic shaft joint of the present invention is providedwith a coupling sleeve 10 and a vibration absorbing member 11, inaddition to the yoke 1 and the shaft 2 mentioned above. Out of thesecomponents, the coupling sleeve 10 is formed from a metal plate such asa steel plate or a stainless steel plate by drawing or the like to havea cylindrical shape as a whole. The coupling sleeve 10 is integrallycomprised of a rotation limiting cylinder 12 which is formed in a halfpart in the axial direction (the left part in FIGS. 1 and 2) closer toone end of the shaft 2 and a retaining cylinder 13 which is formed inthe other half part in the axial direction (the right part in the samedrawings) closer to the middle portion of the shaft 2, with a stepportion 14 therebetween. The coupling sleeve 10 may be formed fromsintered metal.

[0060] The rotation limiting cylinder 12 has a oval-shaped crosssection, and is provided with inner-diameter side engagement surfaces15, 15 which are substantially parallel to each other. Note that in theillustrated embodiment, these inner-diameter side engagement surfaces15, 15 are formed to be convex surfaces each with a partiallycylindrical plane. However, these engagement surfaces may be formed assimple flat surfaces. On the other hand, a pair of outer-diameter sideengagement surfaces 16, 16 are formed on one end portion of the shaft 2(the left end portion in FIG. 1) at two positions on the opposite sidesin the radial direction to be substantially parallel to each other. Inthe illustrated embodiment, these outer-diameter side engagementsurfaces 16, 16 are formed to be flat surfaces which are parallel toeach other, and the one end portion of the shaft 2 to have anoval-shaped cross section. Note that the outer-diameter side engagementsurfaces 16, 16 may be formed as convex surfaces each with a partialcylindrical plane, and the inner-diameter side engagement surfaces 15,15 may be formed as flat surfaces. Such one end portion of the shaft 2and the rotation limiting cylinder 12 are combined concentrically witheach other in a state that the one end portion of the shaft 2 isinserted in the rotation limiting cylinder 12. The inner-diameter sideengagement surfaces 15, 15 are formed to face the outer-diameter sideengagement surfaces 16, 16, respectively, with a gap therebetween in aneutral state that the one end portion of the shaft 2 and the rotationlimiting cylinder 12 are combined with each other as described above andno phase shift is generated with respect to the direction of rotationbetween the shaft 2 and the coupling sleeve 10.

[0061] Also, in the illustrated embodiment, the inner-diameter sidecylindrical surfaces 17, 17 which couple the paired inner-diameter sideengagement surfaces 15, 15 to each other on the inner peripheral surfaceof the rotation limiting cylinder 12 and the outer-diameter sidecylindrical surfaces 18, 18 which couple said paired outer-diameter sideengagement surfaces 16, 16 to each other on the outer peripheral surfaceof the one end portion of the shaft 2 are formed as partiallycylindrical surfaces which are concentric with each other with thecentral axes of the shaft 2 and the rotation limiting cylinder 12 as therespective centers thereof. Then, a pair of guide bushes 19, 19 eachhaving an arched cross section are retained by and between theinner-diameter side cylindrical surfaces 17, 17 and the outer-diameterside cylindrical surfaces 18, 18, respectively. These guide bushes 19,19 are formed of synthetic resin such as polyamide resin orpoly-tetrafluoro-ethylene resin or polyacetal resin or low-frictionalmaterial such as oil-contained metal, so as to serve to support the endportion of the shaft 2 and the rotation limiting cylinder 12concentrically with each other with a little displacement allowed in thedirection of rotation. Such guide bushes 19, 19 are preferably fixedeither to the inner-diameter side cylindrical surfaces 17, 17 or theouter-diameter side cylindrical surfaces 18, 18 by bonding, or the like.

[0062] Also, the retaining cylinder 13 mentioned above is formed to havea larger diameter than that of the rotation limiting cylinder 12. In theillustrated embodiment, a pair of flat portions 20, 20 are formed inthis retaining cylinder 13 at two positions on the opposite sides in theradial direction. Then, the vibration absorbing member 11 is disposedbetween the inner peripheral surface of the retaining cylinder 13 andthe outer peripheral surface closer to the middle portion of the one endportion of the shaft 2. This vibration absorbing member 11 is comprisedof an elastic member 21 and a sliding sleeve 22. The elastic member 21is made of elastic material such as elastomer like rubber, and retainedand fixed to the inner peripheral surface of the retaining cylinder 13by backing, bonding, or the like, so that the positional relation of theelastic member 21 with this retaining member 13 is not changed. Then,the sliding sleeve 22 is retained by and fixed to the inner peripheralsurface of this elastic member 21. This sliding sleeve 22 is formed, asshown in FIG. 3, by a pair of sleeve elements 23, 23 each with asubstantially arched cross section are combined with each othercylindrically with gaps 24, 24 between the end edges thereof in thecircumferential direction. The paired sleeve elements 23, 23 are alsomade of low-frictional material in the similar manner as the guidebushes 19, 19 and retained by and fixed to the inner peripheral surfaceof the elastic member 21 by backing, bonding, or the like.

[0063] The inner peripheral surfaces of the sleeve elements 23, 23 eachis comprised of an inner-diameter side flat surface 25 which ispositioned in the middle part in the circumferential direction andinner-diameter side cylindrical surfaces 26, 26 which are positioned atthe both end portions in the circumferential direction. The pairedsleeve elements 23, 23 are combined with each other to form the slidingsleeve 22, and further, in a state that the one end portion of the shaft2 is inserted (thrust) into this sleeve 22, the inner-diameter side flatsurfaces 25, 25 existing on the inner peripheral surfaces of thesesleeve elements 23, 23 are formed to be parallel to each other so thatthe inner-diameter side cylindrical surfaces 26, 26 are arranged toexist on the same cylindrical surface.

[0064] Now description will be made on the relationship between thedimensions of the sliding sleeve 22 constituted by the paired sleeveelements 23, 23 in a free condition and the dimensions of the crosssection of the end portion of the shaft 2 provided with theouter-diameter side engagement surfaces 16, 16 as described above. Notethat the dimensions of the sliding sleeve 22 in a free condition arethose in a state in which the shaft 2 is not inserted (thrust) into thesliding sleeve 22 and the paired sleeve elements 23, 23 for forming thissliding sleeve 22 are displaced inward in the radial direction of theretaining cylinder 13 based on the elasticity of the elastic member 21.When the outer diameter of the front end portion of the shaft 2 is D2and the diameter of a circle which is formed by the inner-diameter sidecylindrical surfaces 26, 26 existing on the inner peripheral surfaces ofthe paired sleeve elements 23, 23 is R26, this diameter R26 is equal toor a little smaller than the outer diameter D2 (R26≦D2). Also, thedistance D16 between the outer-diameter side engagement surfaces 16, 16formed in the one end portion of the shaft is set to be a little largerthan the distance D25 between the inner-diameter side flat surfaces 25,25 existing on the inner peripheral surfaces of the paired sleeveelements 23, 23 (D16>D25).

[0065] The sliding sleeve 22 which has the above dimensionalrelationship and the end portion of the shaft 2 are combined with eachother, by inserting (thrusting) the end portion of the shaft 2 into thesliding sleeve 22 while displacing the paired sleeve elements 23, 23outward in the radial direction of the retaining cylinder 13 against theelasticity of the elastic member 21. Also, in such combined state, theend portion of the shaft 2 is loosely inserted into the rotationlimiting cylinder 12. Note that, in order to insert this shaft 2 intothe sliding sleeve 22 more easily, the front end edge of the shaft 2 ispreferably to be chamfered (not shown). In a state that the slidingsleeve 22 and the end portion of the shaft 2 are thus combined with eachother, the inner-diameter side flat surfaces 25, 25 on the innerperipheral surfaces of the sleeve elements 23, 23 for forming thesliding sleeve 22 and the inner-diameter side cylindrical surfaces 26,26 are elastically pressed onto the outer peripheral surface of the endportion of the shaft 2 owing to the elasticity of the elastic member 21.

[0066] On the other hand, the distance D5 between the paired restraintplate portions 5, 5 integrally provided in the base portion 4 of theyoke 1 in a free state is set to be equal to or a little larger than thethickness T12 of the rotation limiting cylinder 12 (D5≧T12). Also, acircular through holes 27 a, 27 b are formed at positions which arealigned with each other in portions closer to opening ends of therestraint plate portions 5, 5, so that a bolt 28 can be passed. In astate that the rotation limiting cylinder 12 is inserted up to theinterior part of the base portion 4 to constitute the elastic shaftjoint of the present invention, this rotation limiting cylinder 12 doesnot interfere with the bolt 28 which is passed through the holes 27 a,27 b.

[0067] An operation for constituting the elastic shaft joint of thepresent invention by combining the respective constituent parts asmentioned above will be conducted, for example, in the following manner.That is, the shaft 2 on which the coupling sleeve 10 has been supportedthrough the vibration absorbing member 11 at one end portion thereof,has the other end portion coupled to the front end portion of a steeringshaft 30 through a universal joint 29. The shaft 2 is caused to swingaround the universal joint 29 as the center to be displaced from thisstate to the direction indicated by an arrow a in FIG. 1, so that therotation limiting cylinder 12 of the coupling sleeve 10 is inserted intothe base portion 4 of the yoke 1. Note that another universal joint 33having this yoke 1 is required to be coupled to the input shaft 35 of asteering gear 34 in advance. Since the base portion 4 is formed by thepaired restraint plate portions 5, 5 to be laterally opened, it is noneed of displacing this shaft 2 in the axial direction at the time ofthis insertion. Moreover, even if the axial position of the yoke 1deviates a little from that of the shaft 2, no operation is required tocorrect this deviation.

[0068] When the rotation limiting cylinder 12 is inserted into the baseportion 4 from the state shown in FIG. 1 up to the state shown in FIG.4, the bolt 28 is inserted through the through holes 27 a, 27 b, andfurther, a nut 31 is screwed onto a portion which is the front endportion of this bolt protruding from the outer side surface of therestraint plate portion 5 to be tightly fastened. As a result, thedistance between the paired restraint plate portions 5, 5 is reduced,and the rotation limiting cylinder 12 is tightly sandwiched by andbetween the inner side surfaces of the both restraint plate portions 5,5, whereby the coupling sleeve 10 is coupled and fixed to the yoke 1.Note that in order to prevent the front end portions of the restraintplate portions 5, 5 from excessively bending when the bolt 28 and thenut 31 are tightly fastened together, reinforcement ribs 32, 32 areformed on the partial outer peripheral surface of the rotation limitingcylinder 12 at positions near the through holes 27 a, 27 b at the timeof assembling with the base portion 4.

[0069] An effect of the elastic shaft joint of the present inventionwhich is constituted and assembled as stated above is as follows when arotational force is transmitted while preventing transmission of avibration. In case of the transmission of the rotational force, if therotational force to be transmitted is of low torque, the rotationalforce is transmitted through the elastic member 21 which forms thevibration absorbing member 11 mention above. For example, when therotational force is transmitted from the shaft 2 to yoke 1, a rotationof the shaft 2 is transmitted to the elastic member 21 through thepaired sleeve elements 23, 23 which constitute the sliding sleeve 22.Then, this elastic member 21 is elastically deformed to transmit thisrotational force to the yoke 1. In this manner, when a rotational forceto be transmitted is of low torque, or when a rotational force is not tobe transmitted, the elastic member 21 prevents the transmission of avibration between the yoke 1 and the shaft 2. With respect to thevibration and the displacement in the axial direction, not only that theelastic member 21 is displaced in the axial direction (deformed in theshearing direction), but also that the sliding sleeve 22 slides on theouter peripheral surface of the end portion of the shaft 2, therebyabsorbing the vibration and the displacement.

[0070] It is possible to set coefficients of friction between theinner-diameter side flat surfaces 25, 25 provided on the innerperipheral surface of the sliding sleeve 22 and the inner-diameter sidecylindrical surfaces 26, 26, and the outer peripheral surface of the endportion of the shaft 2 to be small, irrespective of presence or absenceof the elastic member 21. Consequently, it is possible to smoothly andeffectively absorb the vibration and displacement in the axial directiondue to a sliding between the inner-diameter side flat surfaces 25, 25and the inner-diameter side cylindrical surfaces 26, 26, and the outerperipheral surface of the end portion of the shaft 2. Moreover, theabrasion on the inner-diameter side flat surfaces 25, 25 and theinner-diameter side cylindrical surfaces 26, 26 provided on the innerperipheral surface of the sliding sleeve 22 and the outer peripheralsurface of the shaft 2 can be minimized so that the abrasion on both ofthese peripheral surfaces can be also minimized with a long-term use,thereby securing the durability of the elastic shaft joint.

[0071] Also, when the torque of the rotational force to be transmittedis large, the rotational force is transmitted between the shaft 2 andthe yoke 1 based on the engagement between the end portion of the shaft2 and the rotation limiting cylinder 12. More specifically, a part ofthe outer-diameter side engagement surfaces 16, 16 provided on the outerperipheral surface of the end portion of the shaft 2 is caused to abutupon a part of the inner-diameter side engagement surfaces 15, 15 formedon the inner peripheral surface of the rotation limiting cylinder 12.Then, an extra rotational force which can not be transmitted by theelastic member 21 is transmitted between the outer-diameter sideengagement surfaces 16, 16 and the inner-diameter side engagementsurfaces 15, 15. Consequently, the durability of this elastic member 21can be secured satisfactorily without an excessive stress to be appliedon the elastic member 21. Note that a part in which the elastic shaftjoint of the present invention is to be assembled is, as shown in FIG.1, not limited to be on the side of the universal joint 33 for couplingthe input shaft 35 of the steering gear 34 to the shaft 2, but may be onthe side of the universal joint 29 for coupling this shaft 2 to thesteering shaft 30.

[0072] Next, FIG. 5 shows a second embodiment of the present invention.In this embodiment, the total length of a shaft 2 a for constituting theelastic shaft joint is shorter than that in the first embodimentdescribed above, and a shock absorbing member 37 is arranged betweenthis shaft 2 a and a yoke 36 for constituting the universal joint 29 onthe side of the steering shaft 30 in series with respect to the shaft 2a and the yoke 36. This shock absorbing member 37 is formed like abellows made from a metal plate which can be plastically deformed, suchas a soft steel plate or a stainless steel plate, and can freelytransmit the rotational force. However, when an impact in the axialdirection is applied, the total length of this shock absorbing member 37is reduced while absorbing the energy of this impact.

[0073] In the present embodiment, with the shock absorbing member 37provided in such manner, it is possible to protect the driver moreeffectively at the time of crash accident by mitigating the impactapplied on the body of the driver from the steering wheel. That is, whenthe steering gear 34 (FIG. 1) is pressed backward (to the right inFIG. 1) at the time of the crash accident, the total length of the shockabsorbing member 37 is reduced so as to prevent the steering shaft 30from being pushed up backward (to the right in FIG. 5). Consequently,the steering wheel which is fixed to the rear end portion of thissteering shaft 30 is prevented from being pushed up toward the driver,thereby preventing large shock from being applied onto the body of thedriver. Other arrangements and effects are the same as those in the caseof the first embodiment described above.

[0074] Next, FIGS. 6 and 7 show a third embodiment of the presentinvention. In this third embodiment, a stopper is provided between therotation limiting cylinder 12 of the coupling sleeve 10 and one endportion of the shaft 2 to restrict displacement of the rotation limitingcylinder 12 and the shaft 2 in the axial direction within apredetermined range. Consequently, in the present embodiment, engagementholes 38, 38 which are elongated in the axial direction (the lateraldirection in FIG. 6 and the perpendicular direction to the sheet surfacein FIG. 7) are provided on the rotation limiting cylinder 12 at twopositions on the opposite sides in the radial direction thereof, and anengagement pin 39 is supported by and fixed to the end portion of theshaft 2 as being passed through in the radial direction. Then, the bothends of this engagement pin 39 are loosely engaged with the engagementholes 38, 38, thereby preventing the end portion of the shaft 2 frombeing coming off from the rotation limiting cylinder 12.

[0075] In such structure of the present embodiment, it is possible toavoid a trouble, by preventing the end portion of the shaft 2 fromfalling off from the rotation limiting cylinder 12 when the couplingsleeve 10 with the end portion of the shaft 2 attached to one endportion thereof is conveyed or when they are assembled together, causedby the separation of the coupling sleeve 10 from the shaft 2. Otherarrangements and effects are the same as those in the case of the firstembodiment described above.

[0076] Next, FIGS. 8 to 10 show a fourth embodiment of the presentinvention. In this fourth embodiment, there are provided a stopperbetween the rotation limiting cylinder 12 of the coupling sleeve 10 andthe end portion of the shaft 2 to restrict displacement of the rotationlimiting cylinder 12 and the shaft 2 in the axial direction within apredetermined range and a sealing member for preventing permeation ofwater into the coupling sleeve 10. In the present embodiment, thestopper comprises recesses 40, 40 which are formed on the outerperipheral surface of the shaft 2 at two positions on the opposite sidesin the radial direction thereof to be elongated in the axial direction(the lateral direction in FIGS. 8 and 9, and the perpendicular directionto the sheet surface in FIG. 10), and protrusions 41, 41 which areformed by expanding thin portions formed at two positions on theopposite sides in the radial direction of the rotational limitingcylinder 12 inward in the radial direction. In the present embodiment,these protrusions 41, 41 are loosely engaged with the recesses 40, 40 toprevent the end portion of the shaft 2 from falling off from therotation limiting cylinder 12.

[0077] Also, in the present embodiment, a bellows 42 which is made ofelastic material for serving as a sealing member is provided between anopening end portion of the retaining cylinder 13 for forming thecoupling sleeve 10 and the outer peripheral surface of the middleportion of the shaft 2. Further, at an opening end portion of therotation limiting cylinder 12 for forming the coupling sleeve 10, a lidmember 43 which is made of elastic material also for serving as asealing member is provided. Since the inner and outer peripheralsurfaces of the rotation limiting cylinder 12 do not communicate to eachother at a portion at which the stopper is provided and the bellows 42and the lid member 43 are provided as stated, it is possible to preventrust on the outer peripheral surface of the end portion of the shaft 2or increase of sliding resistance of the sliding portion by preventingpermeation of water or invasion of dust or other foreign substances intothe coupling sleeve 10. Other arrangements and effects are the same asthose in the first embodiment described above.

[0078] Next, FIGS. 11 to 14 show a fifth embodiment of the presentinvention. In this fifth embodiment, there are provided elasticrestraint plates 44, 44 respectively outside the outer side surfaces ofthe paired restraint plate portions 5, 5 for constituting the baseportion 4 of the yoke 1 which serves as the rotary member. Consequently,in the present embodiment, a restraint bracket 45 is formed by bendingan elastic metal plate of spring steel, stainless steel, or the like,into a substantially U-shape. This restraint bracket 45 is comprised ofthe paired elastic restraint plates 44, 44, and a coupling plate portion46 for coupling the base edges (the right edges in FIG. 12) of theseelastic restraint plates 44, 44 to each other. A locking hole 47 isformed at a central portion of this coupling plate portion 46. When therestraint bracket 45 is attached to this base portion 4, a lockingprotrusion 48 which is formed on the outer peripheral surface of themiddle portion of this base portion 4 is thrust into the locking hole47. The peripheral edge portion of this locking hole 47 is, under thisthrust state, inserted into the outer peripheral surface of this lockingprotrusion 48, thereby preventing separation of the base portion 4 fromthe restraint bracket 45. Note that the base portion 4 and the restraintbracket 45 may be coupled to each other by a screw or other means.

[0079] In either case, in the state that the restraint bracket 45 iscoupled to the base portion 4, the elastic restraint plates 44, 44 havethe elasticity to come toward the outer side surfaces of the restraintplate portions 5, 5. Also, two locking protruding pieces 49, 49 areprovided at each of the front end portions (the left end portion in FIG.12, and the upper end portion in FIG. 13), that is four in total, of theelastic restraint plate portions 44, 44. Each of these lockingprotruding pieces 49, 49 is cut into a U shape, leaving a part on theside of the front edge of the elastic restraint plate 44, to be bent alittle (making an acute angle) toward the inner side surface of theelastic restraint plates 44. Such locking protruding pieces 49, 49 areautomatically retracted when insertion plate portions 51, 51 which areprovided in a supported bracket 50 described later are inserted intogaps 52, 52 between the outer side surfaces of the restraint plateportions 5, 5 and the inner side surfaces of the elastic restraintplates 44, 44. On the other hand, in the state that these insertionplate portions 51, 51 are in the gaps 52, 52, side edges of theseinsertion plate portions 51, 51 are engaged with the front edges of thelocking protruding pieces 49, 49 so as to prevent the insertion plateportions 51, 51 from falling from the gaps 52, 52.

[0080] On the coupling sleeve 10 fitted on the end portion of the shaft2 via the vibration absorbing member 11, the supported bracket 50 isfitted to be supported on the base portion of the rotation limitingcylinder 12 (the right end portion in FIGS. 11 and 14). This supportedbracket 50 is formed of an elastic metal plate, like the restraintbracket 45 described above, and is provided with a supporting annularportion 53 to be fitted on the base portion of the rotation limitingcylinder 12. Then, each of the base portions of the insertion plateportions 51, 51 is connected to a part of a side edge of this supportingannular portion 53 (the left side edge in FIGS. 11 and 14) which faceseach of the flat outer side surfaces formed on the rotation limitingcylinder 12. These insertion plate portions 51, 51 are extended from thebase portion 50 to be respectively formed into L-shapes. The middleportions to the front half portions of these insertion plate portions51, 51 are formed to be parallel to each other according to the distancebetween the gaps 52, 52 so that they can be freely inserted into thepaired gaps 52, 52. The insertion plate portions 51, 51 can freelyadvance into the gaps 52, 52 while urging or retracting the lockingprotruding pieces 49, 49, and after the advancement, are prevented fromfalling off from the gaps 52, 52 owing to the engagement with theselocking protruding pieces 49, 49.

[0081] The base portion of an elastic stretching piece 54 is connectedto the middle portion of a side edge of the supporting annular portion53 between the insertion plate portions 51, 51. In the state that bothof these insertion plate portions 51, 51 are inserted in the gaps 52,52, the elastic stretching piece 54 is positioned on the opening side ofthe base portion 4 (this side in FIG. 11 and the left side in FIG. 12).

[0082] Further, a bolt 28 a which is a coupling member for coupling theyoke 1 and the coupling sleeve 10 together by reducing the distancebetween the paired restraint plate portions 5, 5 for constituting thebase portion 4 has a slant portion 55 of a conic convex plane in amiddle part thereof. The outer diameter of this bolt 28 a is smaller ata male screw portion 56 which is closer to the front end thereof thanthis slant portion 55, and is larger at a shank 57 which is closer tothe base end thereof than the slant portion 55. A screw hole 58 and acircular hole 59 are formed concentrically at positions which arealigned to each other close to the front ends of the restraint plateportions 5, 5. In the state that the male screw portion 56 of the bolt28 a is threadably engaged with the screw hole 58, out of those holes,the base end portion of the shank 57 is fitted in the circular hole 59without little backlash, and a part on the outer peripheral surface ofthe middle portion of this shank 57 in the circumferential direction isbrought into contact with the elastic stretching piece 54 elastically.

[0083] When the structure of this embodiment is assembled with theabove-mentioned constituent members, the coupling sleeve 10 which isfitted on the end portion of the shaft 2 in advance is thrust from anopening into the base portion 4 of the yoke 1 (from left to right inFIG. 12). The restraint bracket 45 is attached to this base portion 4while the supported bracket 50 to the coupling sleeve 10 in advance.Upon thrusting of the coupling sleeve 10 into the base portion 4 of theyoke 1, the insertion plate portions 51, 51 advance into the gaps 52,52, and upon completion of this advancement, these insertion plateportions 51, 51 can not come out from the gaps 52, 52 owing to theirengagement with the locking protruding pieces 49, 49. Consequently, evenprior to the insertion of the bolt 28 a into the screw hole 58 and thecircular hole 59, the coupling sleeve 10 can not come out from the baseportion 4 freely. For this reason, no troublesome work is required anylonger, such as the insertion of the bolt 28 a which has been conductedwhile supporting the coupling member 10 and the base portion 4 forcoupling the coupling sleeve 10 to the base portion 4, and has beenusually carried out in a limited space. Note that when it is required toseparate the coupling sleeve 10 from the base portion 4, the elasticrestraint plates 44, 44 are elastically deformed to be separated fromthe restraint plate portions 5, 5, whereby the separation work can beconducted without damaging any constituent member.

[0084] When the coupling sleeve 10 is thrust into the base portion 4 ofthe yoke 1 so as to prevent the coupling sleeve 10 from falling out ofthe base portion 4 due to the engagement between the insertion plateportions 51, 51 and the locking protruding pieces 49, 49 as statedabove, the male screw portion 56 of the bolt 28 which is passed throughthe circular hole 59 is screwed into the screw hole 58 to be tightlyfastened further. In the process of this screwing and fastening, theslant portion 55 which is formed on the outer peripheral surface of thebolt 28 a and the elastic stretching piece 54 are brought intoengagement, and the coupling sleeve 10 is elastically pressed upon theinterior surface of the base portion 4 owing to this engagement. Theforms and the sizes of the coupling sleeve 10 and the base portion 4 aredetermined such that the central axis of the coupling sleeve 10 and thatof the base portion 4 meet each other in the state that a part of theouter peripheral surface of the coupling sleeve 10 and the interiorsurface of the base portion 4 are in contact to each other in the axialdirection (the lateral direction in FIG. 11 and the perpendiculardirection to the sheet surface in FIG. 12). The central axis of thecoupling sleeve 10 and that of the shaft 2 also meet each other.Consequently, if the shank 57 of the bolt 28 a presses the couplingsleeve 10 upon the interior surface of the base portion 4 through theelastic stretching piece 54, it becomes possible to easily conduct acoupling work of the shaft 2 and the yoke 4 together while making thecenters of rotation of the both members to meet each other.

[0085] Note that the arrangements, operations, and the like of thecoupling sleeve 10 and the vibration absorbing member 11, which form thebasic structure of the elastic shaft joint 3 to be assembled in thepresent embodiment, are the same as those in the first embodiment shownin FIGS. 1 to 3 described above. The arrangement for facilitating acoupling work of the end portion of the shaft 2 to the base portion 4 ofthe yoke 1 while making the centers of rotation of the both members tomeet each other, as described in the present embodiment, can be realizedas a coupling portion between a yoke of an ordinary universal joint andan end portion of a shaft, even in a structure other than that of theelastic shaft joint embodying the present invention. That is, in somecases, the end portion of the shaft 2 and the base portion 4 of the yoke1 is directly coupled and fixed to each other without interposing thecoupling sleeve 10 or the vibration absorbing member 11 therebetween. Insuch cases, if the supported bracket 50 is attached to the end portionof the shaft 2 at the same time when the restraint bracket 50 isattached to the end portion of the shaft 2, it is also possible toeasily conduct a coupling work of the end portion of the shaft 2 to thebase portion 4 of the yoke 1 while making the centers of rotation of theboth members to meet each other.

[0086] Note that as an arrangement for facilitating a coupling work ofthe end portion of the shaft to the yoke, there are conventionally knownthose disclosed in U.S. Pat. No. 5358350, European Patent No. 0 508 856A1, and the like. However, those conventional technologies require awork of passing a coupling bolt through a yoke and then rotating theyoke together with the shaft, and the like, to make the arrangementcomplicated. If the arrangement of this embodiment is employed, suchtroublesome works can be saved so that it is possible to easily conducta work for coupling the end portion of the shaft 2 and the yoke 4together while making the centers of rotation of the both members tomeet each other.

[0087] Next, FIGS. 15 to 18 show a sixth embodiment of the presentinvention. In this sixth embodiment, locking grooves 60, 60 respectivelyserving as the locking portions are formed on the inner side surfaces ofthe paired restraint plate portions 5, 5 for constituting the baseportion 4 of the yoke 1. Also, a supporting annular portion 53 a isfitted on the coupling sleeve 10, so as to support a supported bracket50 a around this coupling sleeve 10. Then, locking protruding pieces 49a, 49 a are respectively formed in parts of paired insertion plateportions 51 a, 51 a which are provided in this supported bracket 50 a.Each of these locking protruding pieces 49 a, 49 a is cut into a Ushape, leaving a part on the side of the front edge of the insertionplate portion 51 a in the direction of insertion of the insertionthereof, to be bent a little toward the outer side surface of thisinsertion plate portion 51 a. Such locking protruding pieces 49 a, 49 aare automatically retracted (elastically pressed) when the insertionplate portions 51 a, 51 a are inserted into gaps 52 a, 52 a between theinner side surfaces of the restraint plate portions 5, 5 and therespective outer side surfaces of the coupling sleeve 10, together withthe end portion of the shaft 2 on which the coupling sleeve 10 isfitted. On the other hand, in the state that these insertion plateportions 51 a, 51 a are in the gaps 52 a, 52 a, the locking grooves 60,60 are engaged with the front end edges of the locking protruding pieces49 a, 49 a to prevent the insertion plate portions 51 a, 51 a fromcoming off from the gaps 52 a, 52 a.

[0088] An elastic stretching piece 54 a is protruding from the end edgein the circumferential direction of one of the paired insertion plateportions 51 a, 51 a (the upper one in FIGS. 15 and 16) toward the endedge of the other insertion plate portion 51 a. This elastic stretchingpiece 54 a is positioned in a space between the screw hole 58 and thecircular hole 59 which are formed at positions aligned to each other onthe restraint plate portions 5, 5, together with the end portion of theshaft 2 and the coupling sleeve 10, as shown in FIGS. 15 and 16, in thestate that the supported bracket 50 a is inserted between the pairedrestraint plate portions 5, 5 for constituting the base portion 4 of theyoke 1. Then, if the male screw portion 56 of the bolt 28 a which ispassed through this circular hole 59 is screwed into the screw hole 58to be further fastened, the coupling sleeve 10 is elastically pressedupon the interior surface of the base portion 4 on the basis of theengagement between the slant portion 55 and the shant 57 formed on theouter peripheral surface of the bolt 28 a and the elastic stretchingpiece 54 a. That is, in the present embodiment, the shaft 2 and the yoke1 are combined together on the basis of the same effects as described inthe fifth embodiment shown in FIGS. 11 to 14, thereby furtherfacilitating a work of coupling the both members together while makingthe centers of rotation of the both members to meet each other.

[0089] Next, FIGS. 19 to 21 show a seventh embodiment of the presentinvention. In this seventh embodiment, a front half portion 61 having apair of arms 6, 6 and a base portion 4 a having a pair of restraintplate portions 5, 5 are separately formed and then are subjected towelding to be fixed to each other, thereby constituting a yoke 1 a forforming a universal joint. The front half portion 61 and the baseportion 4 a are respectively formed of steel plates by plastic workingbased on pressing. In order to couple the front half portion 61 to thebase portion 4 a, which are formed separately in the above-mentionedmanner, by welding, a coupling annular portion 62 with a cut-away partis provided at the front end portion of this base portion 4 a. Also,there is formed on the base end surface of this front half portion 61 acircular extrusion 63 is formed on which the coupling annular portion 62can be fitted. The coupling annular portion 62 is caused to abut uponthe end surface of this front half portion 61 in the state of beingfitted on the circular extrusion 63 and the abutting part is weldedalong the total length thereof, thereby coupling the base portion 4 aand the front half portion 81 together.

[0090] In the present embodiment constituted as described above, a phasebetween the arms 6, 6 and the restraint plate portions 5, 5 in thedirection of rotation can be set arbitrarily. For this reason, a phasebetween a partner yoke 64 and the restraint plate portions 5, 5 in thedirection of rotation can be also arbitrarily set when the universaljoint is arranged. As a result, the degree of freedom in designing thejoint can be enhanced. Further, it is possible to set optimal values forthe thickness of a steel plate for forming the front half portion 61 andthe thickness of a steel plate for forming the base portion 4 a inaccordance with the strength required for the respective parts. For thisreason, it is possible to reduce the weight of the yoke 1 a bypreventing the thickness from being partially too large. Note that thestructure of the present embodiment can be realized by arbitrarilycombining some of the structures of the foregoing first to sixthembodiments.

[0091] Next, FIGS. 22 to 23 show an eighth embodiment of the presentinvention. In the eighth embodiment, the entire coupling sleeve 10 isdisposed between the paired restraint plates 5, 5 for forming the yoke 1b. That is, the structure of this embodiment is different from that ofthe first embodiment shown in FIGS. 1 to 4 in that the rotation limitingcylinder 12 is omitted and the vibration absorbing member 11 and thesliding sleeve 22 are disposed between the outer peripheral surface ofthe end portion of the shaft 2 and the inner peripheral surface of thebase portion 4 b of the yoke 1 b. According to such structure of theeighth embodiment, the size of an elastic shaft joint 3 a in the axialdirection thereof and, in its turn, the total length of the universaljoint which assembles this elastic shaft joint 3 a therein can bereduced. As a result, a design for effectively protecting the driver canbe achieved more easily by increasing an amount of displacement of theshaft 2 in the axial direction thereof in case of a crash accident. Thestructure of the present embodiment can also be realized by arbitrarilycombining some of the structures of the foregoing first to seventhembodiments.

[0092] Next, FIGS. 24 to 27 show a ninth embodiment of the presentinvention. In the ninth embodiment, a coupling bracket 65 having a pairof restraint plate portions 5, 5 is fixed to an end portion of the shaft2 by welding, or the like, while a shaft 66 having an oval-shaped crosssection is fixed to the base portion of a yoke 1 c by welding, or thelike. Then, the vibration absorbing member 11 and the sliding sleeve 22are disposed between the outer peripheral surface of this shaft 66 andthe inner peripheral surface of the coupling bracket 65. Otherstructures and effects of the present embodiment are the same as thosein the eighth embodiment described above. In the present embodiment, thecoupling bracket 65 is equivalent for the rotary member.

[0093] Next, FIGS. 28 and 29 show a tenth embodiment of the presentinvention. In the tenth embodiment, grooves 67, 67 a for retaininggrease are formed on the inner peripheral surface of a sleeve element 23a for forming the sliding sleeve 22 (see, for example, FIGS. 2 and 3).The grease retained in these grooves 67, 67 a smoothly slides on asliding contact surface between the inner peripheral surface of thesliding sleeve 22 and the outer peripheral surface of the shaft in thestructure with the elastic shaft joint so that the displacement in theaxial direction can be performed smoothly. Note that such sleeve element23 a can be combined with either of the structures of the foregoingembodiments.

[0094] Since arranged and operated as described above, the presentinvention can contribute to realize an elastic shaft joint of practicaluse which can absorb a large displacement in the axial direction andwith a satisfactory secured durability though it can be manufactured ata low cost without requiring complicated processing works.

What is claimed is:
 1. An elastic shaft comprising: a shaft with a pairof outer-diameter side engagement surfaces which are substantiallyparallel to each other at two positions on the opposite sides of theouter peripheral surface in the radial direction: a rotary member with apair of restraint plate portions which are substantially parallel toeach other, having an opening on a lateral side thereof; and a vibrationabsorbing member provided between said rotary member and said shaft,wherein said vibration absorbing member is constituted by an elasticmember disposed on the inner peripheral surface of a part fixed to saidrotary member and a sliding sleeve supported by the inner peripheralsurface of said elastic member, which inner peripheral surface isbrought into slidable contacted with the outer peripheral surface of theshaft.
 2. An elastic shaft joint for coupling an end portion of arotatable shaft to a rotary member for rotating upon a rotation of thisshaft to absorb some displacement thereof in the axial direction and thedirection of rotation, wherein a coupling sleeve is disposed in thevicinity of one end portion of the shaft to be displaced in the axialdirection of this shaft so as to absorb a vibration to be transmitted toand from this shaft, the base portion, out of said rotary member, towhich the end portion of said shaft is to be coupled and fixed, has anopening on the lateral side thereof, and this coupling sleeve isinserted into this base portion through said lateral opening to suppressthis coupling sleeve with this base portion, thereby coupling and fixingthis coupling sleeve to said rotary member.
 3. An elastic shaft jointfor coupling an end portion of a rotatable shaft to a rotary member forrotating upon a rotation of this shaft to absorb some displacementthereof in the axial direction and the direction of rotation, whereinsaid shaft is provided with a pair of outer-diameter side engagementsurfaces which are substantially parallel to each other at two positionson the opposite sides in the radial direction of the outer peripheralsurface of at least one end of the shaft, a coupling sleeve is disposedin the vicinity of an end portion of the shaft to be extended in theaxial direction of said shaft, provided with inner-diameter sideengagement surfaces which are substantially parallel to each other attwo positions on the inner peripheral surface on the opposite sides inthe radial direction in a half part in the axial direction closer to theone end of this shaft to face said outer-diameter side engagementsurfaces with a gap therebetween in a neutral state in which no phaseshift is generated with respect to the direction of rotation betweensaid coupling sleeve and said shaft, a rotation limiting cylinder forlimiting an amount of rotation of said shaft within said couplingsleeve, a retaining cylinder having a larger diameter than that of therotation limiting cylinder is provided in the other half part of saidcoupling sleeve in the axial direction, which is a part closer to amiddle portion of this shaft, a vibration absorbing member is providedbetween the inner peripheral surface of this retaining cylinder and theouter peripheral surface of one end of said shaft for preventing avibration from being transmitted to and from the coupling sleeve in saidneutral state so as to allow a displacement in the axial direction ofsaid shaft with respect to this coupling sleeve, and the base portion ofsaid rotary member to which the end portion of said shaft is coupled andfixed is formed to have a pair of restraint plate portions which aresubstantially parallel to each other and an opening on the lateral sidethereof, and in the state in which the rotation limiting cylinder ofsaid coupling sleeve is inserted between these two restraint plateportions through said lateral opening, these restraint plate portionsare suppressed toward each other, thereby connecting and fixing saidcoupling sleeve to said rotary member.